The present invention relates to a press method and press apparatus for pressing a workpiece formed of a plurality of laminated plates such as core sheets along the lamination direction, thereby joining the plates in a laminated state. For example, the present invention relates to a press method and a press apparatus for a stator core and rotor core used in motors.
For example, Japanese Laid-Open Patent Publication No. 2001-286107 discloses a prior art apparatus for manufacturing a laminated iron core for a motor. This apparatus does not directly press a laminated iron core. According to this apparatus, a laminated iron core is placed on a bench, and rivets are inserted into through holes formed in the laminated iron core. Each rivet is swaged by a pressing pin. Accordingly, the laminated iron core is swaged by rivets. In other words, the laminated iron core is indirectly pressed via the rivets. At the swaging, an inner shaft is inserted into a central hole of the laminated iron core, and an outer holding ring is fitted about the outer circumferential surface of the laminated iron core. The inner shaft and the outer holding ring reduce radial displacements of the core sheets.
According to the apparatus of the above publication, a laminated iron core is placed on the bench with rivets inserted in the holes in advance. Therefore, radial movement of each core sheet is restricted by the rivets, which prevents the core sheets from being displaced. However, when no rivets are attached to the laminated iron core, there can be problems. In such a case, a laminated iron core formed simply by laminating core sheets is placed on the bench without inserting rivets. When this laminated iron core is subjected to a working operation such as pressing, displacement of the core sheets, if any, will possibly be irreparable. That is, when the laminated iron core is subjected to some sort of working operation, the laminated iron core on the bench is in a fixed position even if the positions of the inner and outer circumferential surfaces of the laminated iron core are restricted as in the apparatus of the above publication. Thus, the laminated iron core cannot be moved, and the core sheets cannot be easily moved to proper positions. Accordingly, it is difficult to produce a high-precision laminated iron core with uniform magnetic flux density.